The disclosure relates generally to turbomachines, and more particularly, to a combustion bypass passive valve system for a gas turbine.
A gas turbine generally includes a compressor section that produces compressed air that is subsequently heated by burning a fuel in the reaction zone of a combustion section. The hot gas from the combustion section is directed to a turbine section where the hot gas is used to drive a rotor shaft to produce power. The combustion section typically includes a casing that forms a chamber that receives compressor discharge air from the compressor section. A number of combustors typically are disposed in the chamber and receive the compressor discharge air along with the fuel to be burned. A duct connected to the aft end of each combustor directs the hot gas from the combustor to the turbine section.
Due to rising fuel costs and other factors, gas fired power plants that were designed to operate at mostly full power output are now being operated on an intermittent basis. For example, a gas turbine may be used only during the daytime and then taken off line during the nighttime when the power demand is lower.
During load reductions, or “turndowns,” combustion systems often must be capable of remaining in emissions compliance down to about fifty percent (50%) of full rated load output, or “base load.” In order to maintain acceptable fuel-to-air ratios at the required turndown levels and to control the formation of oxides of nitrogen (NOx) and carbon monoxide (CO), considered atmospheric pollutants, a portion of the compressor discharge air from the compressor section may be bypassed around the combustors.